1. Field of the Invention
The present invention relates to an ink tank and an ink jet recording apparatus using the aforesaid ink tank.
2. Related Background Art
An ink jet recording apparatus has an advantage that high-speed recordings can be performed quietly with a low running cost. In recent years, therefore, the ink jet recording apparatus has been in use in many ways as the recording apparatus for a copying machine, facsimile apparatus, and the like, the printer for a word processor, electronic typewriter, and the like, or the image output terminal for a computer and the like.
In an ink jet recording apparatus such as this, there are the so-called serial printer type wherein the recording is performed while the recording head is being scanned in the predetermined direction with respect to the recording medium, and the line printer type using the full multitype recording head in which the discharging ports are aligned to cover the entire region corresponding to the full width of the recording medium. Particularly, the former is such that its recording head itself performs the operation (the reciprocal motion along the platen roller), and a structure such as given below is often employed.
In the ink jet recording apparatus, liquified ink is supplied from an ink supply source to the recording head main body. At this juncture, in the recording head used for the serial printer type recording apparatus, a sub-tank, which is detachably connected to the recording head, is provided as an intermediate reservoir member in the ink supply system for the recording head in such a manner that this sub-tank is allowed to scan together with the recording head. This sub-tank is not filled with ink completely in its inside but is used with a predetermined amount of air reserved therein. Then, with the existence of this air portion, the shock generated by the motion of the ink head at the time of recording or at the time of the head coming to a stop is softened to prevent the ink leakage from the discharging port due to such shock or the ingression of air into the discharging port.
Here, the mode of the sub-tank will be described.
FIG. 9 is a plan view showing an example of the sub-tank arranged in a conventional recording head, and FIG. 10 is a cross-sectional side view thereof. In FIG. 9 and FIG. 10, a reference numeral 117 designates the entire body of the sub-tank; 117a, the induction outlet of an ink supply tube for supplying ink to the recording head; 117b, the connecting portion of the tube (sub-tank tube) communicated with a suction means for sucking air or ink in the sub-tank 117 therethrough; and 117c, an induction port for the ink supply. Also, the dashed line represents the actual liquid level (horizontal plane) to be formed when the sub-tank is installed in the carriage in the main body of the apparatus.
The height, measured from the bottom face of the tank, of the induction outlet 117a of the ink supply tube for supplying ink contained in the sub-tank 117 to the head is lower than the connecting portion 177b to the sub-tank tube. By actuating the suction means to induce ink into the sub-tank 117 from the induction port 117c, it is possible to perform a stable ink supply because the liquid level is usually positioned sufficiently higher than the induction outlet 117a of the supply tube to the head. Also, the structure is arranged so that a reservoir of air is always maintained above the connecting portion 117b to the sub-tank tube.
Usually, at the time of recording (printing) with the sub-tank 117 being installed in the carriage of the main body of the apparatus, the ink contained in the sub-tank 117 maintains the liquid level represented by the dashed line in FIG. 10. Then, a substantially equal amount of ink to that of the ink consumed by the head is refilled from the ink supply source through the ink inlet 117c because the sub-tank 117 is a closed system.
Now, in the serial printer, while the printing is performed by causing the recording head to travel, the ink supply system (the supply tube connecting the ink supply source and the sub-tank, for example) swings at that time, and if no sub-tank is provided, ink in the recording head is compressed or decompressed due to ink in the swinging supply tube. However, if the sub-tank 117 with the air reservoir therein is provided, it is possible to prevent the fluctuation of the pressure exerted on the ink in the recording head by the damper effect thereof; thus making stable printing possible.
Nevertheless, for a modern ink jet recording apparatus, a higher speed printing is required. Accordingly, the motion of the recording head has become increasingly quicker and more intense as a matter of course. Therefore, the motion of the supply tube and the like accompanying the recording head in scanning is more intense, leading to the necessity of a sufficient air reservoir.
In the above-mentioned ink jet recording apparatus under the conventional art, however, there is a problem as described below.
In order to obtaining a sufficient air reservoir, the liquid level in the sub-tank 117 is arranged at a position considerably low in the inner space of the sub-tank 117 while the motion of the recording head is quick and considerably violent. Consequently, when the entire body of the sub-tank 117, which integrally travels to scan, swings violently, ink and air in the sub-tank 117 are allowed to mix.
As a result, there is a possibility that air is carried into the recording head through the supply tube to the head when bubbles generated by such mixture approach the induction outlet 117a for carrying ink in the sub-tank 117 to the head.
There is known a structure disclosed in Japanese Utility Model Laid-Open Application 54-48652 (Applied in Japan on Sept. 10, 1977 and Laid-Open on Apr. 4, 1979), i.e., a structure whereby the inside of the ink tank installed in the head carriage is divided into a plurality of tank chambers by partition plates. However, there is still a possibility that bubbles are carried into the recording head once babbles are generated by the vibration.
There is also considered a structure as shown in FIG. 7 and 8 thereby to prevent the mixture of air and ink by vibration with the provision of an inner wall 117d in the sub-tank 117. There is still a possibility that air is not sufficiently prevented from reaching the induction outlet 117a to the head.